Technical Analysis: The Brief Saga of Carbon-Fiber Wheels in the Premier Class

by Marc Seriau/paddock-gp

The story of carbon rims in MotoGP, once the World Speed Championship, led by Honda and Cagiva, lasted only a few years. Long considered one of the most cutting-edge technologies, they were eventually banned by the FIM.

Promising weight reduction, lower inertia, and a reduced gyroscopic effect—and therefore improved handling—they caught the attention of several manufacturers, starting precisely with Honda and Cagiva, before disappearing from Grands Prix for good. Their ban, however, did not stem from a spectacular accident, but rather from a gradual evolution of the technical regulations, officially aimed at reducing costs and increasing safety.

The name Honda is often associated with the development of carbon rims with the NR500 (1979–1983), NR750, and the early NSR500 models. But in 1984, of the four riders who competed in the World Championship under contract with Honda—Freddie Spencer, Randy Mamola, Ron Haslam, and Takazumi Katayama—only Spencer benefited from the NSR500, a race bike equipped with a brand-new V4 engine, while the other three rode the NS500, a conventional model with a 3-cylinder engine.

The first generation of the NSR500, development code NV0A, made its racing debut at the Daytona 200 in March, the most prestigious event in the American motorcycle championship. Despite numerous teething problems due to the engine architecture, it secured pole position in qualifying, with the 499.2 cc bike outpacing the Daytona-only 695 cc Yamaha YZR700 ridden by Kenny Roberts. It finished second and was then entered in the world championship, which began at Kyalami in South Africa. During the first qualifying session of the opening round of the championship, the bike’s rear wheel broke, causing an unexpected crash for Freddie Spencer. He suffered a ligament injury to his right ankle and a fracture to the little toe on his left foot, forcing him to withdraw from the first race of the season, despite being the reigning champion.

At the time, HRC race bikes used Comstar rims, specific wheels designed by Honda. The rim and wheel disc of the NV0A were single-piece parts made of CFRP (carbon fiber reinforced polymer) joined by metal elements. Although HRC had used these carbon Comstar rims since the previous generation, the NS500, some feared they would not withstand the greater power of the NSR500’s V4 engine and might break. The damaged wheel had been used in the previous Daytona race. The bike had fallen on that occasion, but still managed to continue the race. According to HRC’s analysis, the damage likely worsened in the final laps, and the wheel failed before reaching South Africa. The Japanese manufacturer then halted the experiment, considering the risk/benefit ratio unfavorable.

In the early 1990s, Cagiva bikes competing in the 500cc class already used carbon fiber frames and rims, designed by Piero Ferrari (Enzo’s son). The goal was clear: to reduce unsprung mass and gyroscopic inertia to improve the bike’s responsiveness in corners. At that time, Cagiva was multiplying technical innovations in an effort to compete with Honda, Yamaha, and Suzuki. The carbon wheels (3.5 x 17 inches and 6.0 x 17 inches) on the C593 were part of this pursuit of performance (as were the subsequent next-generation aerospace-derived aluminum frames and the 320 mm carbon-carbon discs).

However, as with other manufacturers, the benefits were offset by several drawbacks: very high production costs (in Ferrari’s case), delicate maintenance, and above all complex inspection after a collision, a somewhat harsh brush with the curbs, or even a simple tire change… Unlike a light-alloy rim that can deform, a carbon rim can suffer invisible internal damage from a simple impact against a curb or during a tire change. These micro-fractures are difficult to detect and can therefore lead to sudden failure at any time. Added to this are the high production costs and the greater complexity of maintenance during Grand Prix weekends, where wheels are repeatedly removed and reinstalled.

These significant limitations, together with other minor issues such as heat transfer, along with advances in forged magnesium rims produced by Dymag and later by Marchesini, greatly reduced the advantages of composite wheels, even in terms of weight. The FIM therefore did not have to ban carbon wheels following an accident, but did so much later for economic reasons. The first step came with the creation of Moto2, at a time when MotoGP was far less high-profile than today, as evidenced by the creation of the CRT, the so-called “bastards”... On December 11, 2009, the Grand Prix Commission published the technical regulations for the new category, which from the outset banned wheels made of composite material. Moto3, created in 2012, immediately adopted the same rule. MotoGP, however, remained authorized to use this type of wheel until the end of the 2012 season.

The turning point came during the Grand Prix Commission meeting on December 13, 2012 in Madrid. The official statement simply reads: “Carbon composite rims are not permitted. (As already in Moto3 and Moto2).” From the 2013 regulations onward, the provision was extended to all categories: “Rims with a composite structure (in particular those made of carbon fiber, fiberglass, or any other similar composite material) are not permitted.” This ban was also part of the cost-containment policy pursued by Dorna and the FIM in the early 2010s, which would lead to the introduction of the single ECU, engine limits, and several other technical restrictions (with the notable exception, of course, of the very expensive seamless gearboxes...).

Carbon rims had a relatively short period in Grand Prix racing, but remain associated with an era when manufacturers explored the boldest solutions without setting limits.

Honda, and also Cagiva, played a decisive role in demonstrating the potential of this technology. Although carbon rims have disappeared from world circuits, they remain a symbol of the innovation that characterized the 500cc prototypes of the 1980s and 1990s.

Today, the regulations allow only magnesium or aluminum alloy rims, definitively closing the chapter on composite rims in the World Speed Championship.